This invention relates to marine anchors and, more specifically, to a twin-fluke, lightweight, high performance aluminum anchor having removable twin flukes and a unique monolithic crown structure with the holding power and structural integrity of heavier steel anchors.
The anchor is an improvement over the anchors described in U.S. Pat. Nos. 2,249,546; 2,320,966; 2,641,215 and 2,643,631 to Danforth, U.S. Pat. Nos. 3,771,486; 3,780,688; 3,822,665 and 3,858,543 to Hungerford and U.S. Pat. No. 2,840,029 to Ogg, all having generally a shank, a stock and a pair of twin flukes coupled together by a crown structure.
When the anchor is resting on the underwater bottom, the anchor line or rode connects a boat or other marine vessel floating on the surface to the outer end of the shank. The anchor rode will pull the anchor forward along the bottom as the marine vessel drifts with the wind or tide. The crown structure resting on one side of its two crown plates tends to resist the forward motion, as well as elevating the after end of the anchor, thereby tipping the anchor such that the fluke tips are oriented downward toward bottom. As the anchor is drawn forward, the flukes will tend to bury themselves deeply into bottom. As the force on the rode is increased, the flukes will continue to bury themselves deeper and deeper into bottom, thus providing greater and greater holding power. It is not uncommon for a properly designed anchor to bury itself to the point where its uppermost surface is several feet under bottom. This condition has been observed in bottoms of mud, sand and even hard sand.
When attempting to set the anchor, the shank will pivot on the stock. In order to quickly set the anchor, it is desirable that the shank be able to rotate to provide an angle of 30.degree.-35.degree. relative to the effective surface of the flukes. If the angle is too great, the anchor will have difficulty in initially beginning the process of burying itself and, once begun, will likely become shod. That is, the planar portion of the flukes will likely become caked with mud, which will substantially reduce the anchor's holding power. If the angle is too small, the flukes will not be able to deeply penetrate the bottom since the burying resistance of the shank, crown and stock is working against the effective fluke surfaces which provide the burying forces. The maximum angular rotation of the shank in either direction is limited by contact with the crown.
A problem, especially prevalent with prior art lightweight anchors, is deformation and/or failure of the crown structure due to the concentrated force exerted by the shank on the crown plates. These forces tend to cause the plates to deform and/or structurally fail where the shank makes contact. As the deformation progresses, the angular rotation of the shank increases, greatly reducing the anchor's holding power. Eventually, the plates will separate from the supporting side walls, rendering the anchor unusable. The prior art has suggested some solutions to this problem, e.g., the use of heavier material such as steel or the use of exotic assemblages designed to spread the force exerted by the shank over a wide area, as shown in the Hungerford U.S. Pat. No. '486 patent. However, these prior art solutions introduce additional problems due to the additional weight and/or complexity and, most importantly, increase the burial resistance area and shape. The anchor's ability to have high holding power requires that the flukes be capable of burying the entire anchor including the crown, shank and stock to such a depth that the flukes have found their way down into the hard relatively compact bottom. It, therefore, is important that the resistance to the burying of the crown structure be minimized without sacrificing strength.
Additionally, due to the open box-like structure of the typical prior art crown structure, large amounts of mud, rocks or other debris will accumulate within the structure while the anchor is being set. The debris adds to the burying resistance as well as adding considerable weight to the anchor, making retrieval of the anchor very difficult. Of equal concern to the burying resistance is the restriction of the angular rotation of the shank when the anchor is broken loose due to a 180.degree. change of wind or tide.